共查询到19条相似文献,搜索用时 171 毫秒
1.
2.
3.
基于扩散模型方程和集总参数模型方程,首次建立了具有3个可调参数的两步扩散模型方程.该模型同时考虑固体颗粒内扩散阻力与内壁的阻力,能较好地描述超临界流体萃取过程.用两步扩散模型方程模拟了超临界CO<,2>萃取丁香油的动态过程,在实验温度与压力范围内模型计算值与实验数据的平均相对误差AARD在2.33%~19.48%之间,所有实验点的AARD为8.09%.而用扩散模型方程和集总参数模型方程模拟,所有实验点的AARD分别为17.51%和8.13%,表明两步扩散模型对于超临界CO<,2>萃取丁香油的传质过程的模拟效果优于扩散模型方程和集总参数模型方程. 相似文献
4.
5.
6.
通过高压吸收法可以将生物质超临界水气化制氢的气体产物中的CO2与H2分离.基于修正的UNIFAC模型、SRK状态方程以及MHV2混合规则,建立了生物质超临界气化制氢产物高压吸收法分离的气液相平衡的计算模型,讨论了CO2与H2分离过程中压力和温度等参数对分离效果的影响.计算结果表明:随着分离器中压力的升高,气相产物中H2的摩尔分数增加,CO2摩尔分数迅速下降,气相中H2的收率不断降低;随着温度升高,气相产物中H2的摩尔分数减小,CO2摩尔分数上升,气相中H2的收率增加;然而,高压吸收的方法不能将气体产物中的CO、CH4、C2H4、C2H6与H2分离. 相似文献
7.
8.
聚合物中杂质/挥分的存在对聚合物的终端使用将产生负面影响,因此必须将其除去.传统的脱挥方法效率有限,使用超临界流体技术可增强脱挥效率.测定了温度为343 K、压力为30 MPa、CO2流量为4.0 L8226;min-1条件下,PET聚酯薄膜中的乙二醇单体挥分含量与时间的关系,以研究聚合物系超临界流体脱挥过程中的质量传递规律;根据传质理论建立了一个理想的超临界流体脱挥过程的质量传递模型,并用该模型分析处理实验数据,结果表明该模型较好地反映了聚合物系超临界流体脱挥过程的基本特征. 相似文献
9.
10.
超临界CO2萃取丁香油的数值模拟 总被引:1,自引:1,他引:0
为了预测超临界CO2萃取挥发油动态过程,根据挥发油在超临界CO2与物料之间的质量传递平衡,采用集总参数法建立超临界CO2萃取丁香油过程的数学模型。结合不同温度、压力、粒径和CO2流速条件下的实验结果,对方程进行了合理的简化,并利用实验数据拟合出模型中CO2密度、粒径和流速的系数。验证结果表明模型的计算值和实验值的平均相对误差在6. 88%~57. 78%之间,建立的数值模型能较好地描述实际的超临界CO2萃取丁香油行为。 相似文献
11.
超临界流体萃取动力学模型(Ⅰ) 总被引:9,自引:0,他引:9
综述了目前用超临界流体从植物体中萃取油脂成分的萃取过程机理,建立了模型的假设条件以及不同籽油的萃取动力学模型,分析了传质过程的推动力和阻力、体积传质通量的表达式以及模型参数的计算和关联。 相似文献
12.
An unsteady-state mathematical model describing supercritical fluid (SCF) delignification of wood in a packed bed was developed. Equations describing intraparticle supercritical methyl-amine reaction with lignin, and subsequent transport of the methylamine-lignin complex into the bulk phase were derived and solved using orthogonal collocation. Model results for the case of supercritical methylamine are presented and compared with experimental results. Simulation results correctly predicted the experimental results. Sensitivity of methylamine extraction of lignin was evaluated by varying bulk fluid velocity, mass transfer coefficient, and particle diameter. Delignification was a strong function of particle diameter and a relatively weaker function of fluid velocity and mass transfer coefficient. The Thiele modulus and Biot number showed that delignification was reaction rate limited for wood particle diameter values ≤ 0.1 cm, but delignification was limited by intra-particle mass transfer for wood particle diameter values ≥ 1.0 cm. 相似文献
13.
《The Journal of Supercritical Fluids》2009,47(3):285-292
This article reports the achievements of the micro-scale (secretory-structure-scale) mathematical modelling of essential oil isolation by supercritical carbon dioxide. Some new experimental and modelling results are presented. The improved model for the supercritical fluid extraction from the glandular trichomes (peltate glands) is introduced. According to the behavior of plant secretory structures during the extraction as well as according to the modelling results, plant material was classified according to the dominant resistance to mass transfer during the extraction process. External mass transfer was the rate limiting step in the extraction from plants with secretory ducts and secretory cavities of citrus family. In the case of extraction from secretory cells, internal diffusion was the rate limiting step. In the extraction from glandular trichomes, external mass transfer, as well as diffusion through the gland membrane influenced the process. 相似文献
14.
设计了超临界流体萃取塔系统,并对其流体力学特性和传质性能进行了研究,为工业设计提供了理论依据。在连续逆流操作的超临界填料萃取塔、筛板萃取塔和喷淋萃取塔中,应用超临界二氧化碳-异丙醇-水、超临界二氧化碳-乙醇-水两种实验体系对流体力学模型和传质模型进行了实验验证,计算结果与实验数据符合较好。 相似文献
15.
16.
17.
The experimental feasibility of mannitol extraction from olive leaves using supercritical carbon dioxide was investigated. The experimental data indicated that increasing the pressure from 200 to 350 bar and decreasing the temperature from 80 to 40 °C resulted in an enhancement of the extraction yield and reduced the partition coefficient significantly. In addition, increasing the extraction time from 10 to 90 min increased the extraction yield, while further increases up to 180 min did not cause any further change. Ethanol was utilized as an entrainer and the maximum extraction yield was obtained using 20 % of ethanol. Moreover, modeling of the supercritical fluid extraction was carried out with the relevant mass transfer mechanisms involved in the supercritical and solid phases, and the appropriate numerical method of finite difference. The numerical results show that the model with three adjustable parameters is capable of predicting the experimental data very well. 相似文献
18.
The dynamic behavior of supercritical fluid extraction (SFE) of valerenic acid (VA) from valerian (Valeriana officinalis L.) roots was studied by mathematical modeling. The extraction yield of VA was considered as the most desirable compound among the other extracted constituents. A two‐phase desorption model was developed by considering a diffusion controlled regime in the particle and axial dispersion in the bed. The mass transfer parameters, i.e., pore diffusivity, film mass transfer coefficient and axial dispersion, along with the solubility parameters were chosen as the model parameters. The first three mass transfer parameters were predicted using nondimensional equations from the literature. The solubility equation and the parameters were studied using different equilibrium models, i.e., Henry, Langmuir, Freundlich, Langmuir‐Freundlich (L‐F) and Toth isotherms. The equilibrium parameters were correlated by comparing the outlet results of the dynamic SFE model with experiments. The experimental yield of the VA extraction was obtained at a pressure of 15.0–36.0 MPa, temperature of 310–334 K, solvent flow rate of 0.50–1.10 · 10–6 m3/min and different particle sizes ranging from 0.18–2.00 · 10–3 m in diameter, at a 20 min constant static period, in the presence of 46.9 μL/g ethanol as the co‐solvent, followed by dynamic time extraction for up to 50 min. From the results, the mathematical model using the L‐F equation exhibited the best agreement with the experimental yield of VA extraction in the range of studied conditions. The present model can be applied to design and scale up the SFE process of VA from Valeriana officinalis L. roots. 相似文献
19.
A computational fluid dynamics model of extraction of a solute (caffeine) from a porous solid matrix (coffee beans) using a supercritical solvent (carbon dioxide) is developed. Supercritical fluid extraction of a solute from a solid matrix is a slow process even when solute free solvent is circulated. The use of acoustic waves represents a potential efficient way of enhancing mass transfer processes. The effect of acoustically excited flows on supercritical fluid extraction from a porous solid matrix is investigated. The mathematical model considers diffusion-controlled regime in the porous solid matrix and convective-diffusive transport in the bulk fluid. Henry's law is used to describe the equilibrium states of the solid and the fluid phases. Accurate representation of the thermo-physical properties of supercritical solvent is considered by using the NIST Standard Reference Database 12. The conservation equations for mass, momentum, energy and species are numerically solved using implicit finite volume method. The effect of process parameters, such as initial state (pressure and temperature) of solvent and acoustic waves on the yield of solute extraction is also investigated numerically. 相似文献